In order to make the flow of goods transported on a conveyor more uniform when the feed rate is random queues have been developed which fill up and are emptied without it being necessary to stop the conveyor itself.
There are numerous methods of accumulating loads on a conveyor the simpliest of which uses the gravity acting on the loads themselves. The major drawback of this method is that it creates a line pressure proportional to the slope and the total weight of the accumulated loads. If a power conveyor is used and the loads idle on the conveyor a considerable line pressure also results which depends on the friction of the loads on the conveyor.
In accordance with other known methods of accumulation the conveyor is operated intermittently by loading an upstream conveyor while unloading a downstream conveyor, or even by using a number of conveyor modules equal to the number of loads to be accumulated.
Among known accumulator conveyors reference is made to disconnectable conveyors which are automatically disconnectable in response to rollers simultaneously urged by a drive member and blocked by the accumulating loads. The great drawback of these conveyors is that they are difficult to control and require extra thick portions on the driven member to assure the periodic starting of the rollers thereby developing a certain line pressure. There are also conveyors which are disconnectable by load sensing means, these sensing means enable one section of the conveyor to be disconnected when there is a load on it or reconnect this section when the load clears the same. In these devices the connect/disconnect function is accomplished by actuating means which may be pneumatic, electric or even hydraulic. Even though these are high performing devices they have the great drawback of having a prohibitive cost.
On the other hand purely mechanical connect/disconnect systems are generally simpler and therefore more economical and rugged.
Accumulation conveyors of this type have already been disclosed, namely, in French Pat. No. 1,225,981 which describes a conveyor comprising a roller level which bears the load and a central drive belt driving the rollers, the driving of the conveyor being section by section by lifting the belt above the transport surface of the loads so as to bear against the loads, or by lowering below the transport surface, sensing means detecting the presence of loads controlling the device.
The major drawback of this type of conveyor is that it does not accept a very wide range of weights per unit length. In fact the connect/disconnect means is coupled to the sensing means by a set of levers so that there is a linear relation between forces necessary for actuating the sensing means and those which may be exerted by the connect/disconnect unit and the drive belt on the loads to be transported. Consequently, if the sensing means are adjusted so that light loads may be sensed a rather small drive force is obtained which is insufficient for heavy loads transported. Conversely, if the sensing means are adjusted for heavy loads then light loads are not detected by the sensing means.
Improvements in this known accumulator conveyor enable the drawbacks to be obviated by independently adjusting the pressure exerted by the load sensing means and the pressure exerted on the connect/disconnect means of the drive member.
One of these known devices which comprises cams with flats for urging the drive member against the carrier rollers results in very noisy operation owing to the fact that upon each rotation of the cams the drive element moves up and down and strikes the carrier rollers. Further, during load accumulation the drive belt for the carrier rollers rubs against the flats of the cams which consumes energy, wears the belt and increases the force required for reconnecting the mechanism.
With a view to improving this existing accumulator conveyor a double cam system has been developed which is markedly less noisy owing to the fact that the belt is not subjected to a pulsating movement and does not beat against the carrier rollers but during load accumulation the belt still rubs against the flats of the double cam with the aforesaid attendant drawbacks.